Investigations have shown that menarche in the human female is occurring 3-4 months earlier each decade. Work on a variety of mammalian species suggests that four major categories of factors can affect the age of sexual maturation: social, genetic, nutritional and climatic. Experiments using rodents as models have assessed the individual importance of some of these factors. The proposed research will extend these findings by examining a number of major factors in separate experiments and by testing multiple levels of five major factors in a multi-factor design. The proposed sequence of investigations will use house mice as subjects and four dependent variables; (1) first vaginal estrus, (2) vaginal introitus, (3) uterine weight and (4) body weight, to determine the role of various factors in affecting the timing of sexual maturation. These parameters will include, (1) quantitative and qualitative aspects of diet, (2) temperature and daylength and (3) inhibitory and acceleratory social factors. In addition the degree of genetic inheritance of the timing of sexual maturation will be studied using selection techniques and quantitative analysis. The ultimate goal of the experimental sequence will be to test the interaction and relative importance of these numerous major factors in a multi-factor experimental design. The proposed research has two important aspects of significance for humans. Puberty is an important stress point in the life of a young person - it is therefore necessary that we understand what factors control the timing of sexual maturation and why the age at menarche has been decreasing so dramatically. With the discovery of pheromones in non- human primates it is becoming evident that man too may produce pheromones - it will thus be important to understand the mechanisms of production and function of such pheromones in other mammals if we are to evaluate their potential significance for humans.